Technical Abstract:
The repeated appearance of drug-resistant strains of coccidia has been the impetus for developing alternative methods to control avian coccidiosis. One approach has been vaccination of broiler chicks with low doses of virulent, precocious, or irradiated Eimeria spp. oocysts. The present study was undertaken to determine if vaccination of chickens with irradiated coccidia was a viable approach to controlling avian coccidiosis in a medium-size broiler operation. Fecal material was collected from individual 10,000 ft2 broiler houses in each of two poultry operations containing about 11,000 chickens per house. The samples were processed for eimerian oocysts, extracted for DNA, and analyzed by PCR to examine the composition of Eimeria species in each operation. All seven major Eimeria species- E. acervulina, E. brunetti,E. maxima, E. mitis, E. necatrix, E. praecox, and E. tenella were detected. Vaccine trials using non-irradiated dlaboratory strains of E. acervulina, E. maxima, and E. tenella, plus the the oocyst mixture from each broiler operation were conducted in broiler chickens. All chickens, including unvaccinated controls, were challenged 4 weeks later with field-strain oocysts isolated and amplified from both operations. Protective immunity against field strain coccidia was elicited by vaccination with laboratory strains of E. acervulina and E. tenella, but not with E. maxima possibly reflecting immunovariability between E. maxima isolates. The field strain of E. maxima present in the two poultry operations was single oocyst-isolated, amplified in susceptible chickens, and is being tested in vaccine trials for protection against the field strain oocysts with the goal of using irradiated E. acervulina, E. tenella, and E. maxima and possibly other species against avian coccidiosis.